In the prior art (magnetic disk memory systems) read/write heads are guided across a plurality of tracks on a magnetic disk to effect either reading, or writing, of information from, or onto, that disk, by virtue of a linear track positioner system or by a rotary arm positioner system. Rotary arm positioner systems have many advantages over linear track positioner systems. In a rotary arm positioner system there are fewer problems or considerations, related to friction, because, for one reason, there are fewer bearings. In addition, there are less elements to wear in a rotary arm positioner system. The reflected inertia to the driving means in a rotary arm positioner system is less than in a linear system and hence the rotary arm positioner system can employ smaller motors. The smaller arms of the rotary arm positioner system permits the design of more compact disk drives. Rotary arm positioner systems have fewer parts in the spindle, casting, positioner disk and head thermal circuit which makes thermal expansion and thermal hysteresis more predictable and consistent.
However, while rotary arm positioner systems can be designed to be balanced about their axis of rotation, which makes them insensitive to shock and vibration in the plane of the disk, such a design increases the moment of inertia and affects the access time adversely. The biggest drawback of a rotary arm positioner is the skew, or yaw, angle at which the read/write head has to fly on different radii of the disk. Yaw angles of up to +/-15.degree. have been implemented. However, this has not been considered satisfactory for the most part. The present invention basically combines all of the advantages of the linear track positioner system and all of the advantages of the rotary arm positioner system with virtually none of their disadvantages.